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Publications - Occasional Papers

Glaciers and the Changing Earth System: A 2004 Snapshot

INSTAAR Occasional Paper 58

2005, 116 pp. (cost: $10)

Glacier changes are having impacts on processes of global importance such as sea-level rise, hydrology of mountain-fed rivers, freshwater balance of oceans, and even the shape and rotation of the Earth. Here we discuss the effects of “small glaciers” — all perennial ice masses other than the Greenland and Antarctic ice sheets. We now estimate that the total area of these glaciers and ice caps to be about 785 ± 100 x 103 km2, somewhat larger than earlier estimates because of improved information on isolated glaciers and ice caps around the periphery of the large ice sheets. We estimate the total volume of this ice to be about 260 ± 65 x 103 km3, equivalent to 0.65 ± 0.16 m of sea-level rise.

Glacier mass balance data (both annual and seasonal) can be used to infer current climatic change in precipitation and temperature, and the spatial distribution of these can assist in the analysis and modeling of climate change. This is especially important in high-mountain and high-latitude areas, where precipitation data are few and biased. Air temperature increase is the major forcing of glacier change. Glacier response to recent climate warming shows a steepening mass balance gradient with altitude due to increasing ice ablation below the equilibrium line altitude, and, to a lesser extent, increasing snow accumulation above that altitude. Observational results also show increasing glacier mass turnover and mass balance sensitivity to air temperature; these changes are not predicted by existing climate/glacier models. Sensitivity and turnover have also decreased in variability starting at the end of the 1980s.

Glacier wastage caused sea level to rise at a rate of 0.51 mm yr–1 for the period 1961– 2003, but glaciers are now (1994–2003) causing sea level to rise 0.93 mm yr–1. This freshwater addition to the oceans may be affecting ocean circulation and ocean ecosystems, and causing socio-economic impacts due to sea-level change. This contribution from glaciers is likely to continue to increase in the future. Acceleration of glacier wastage also affects other global processes, including spatial and temporal changes in Earth’s gravitational field, Earth oblateness and rotation rate, and regional uplift.

Global acceleration of glacier volume losses has affected the freshwater cycle at many scales, from global to local. The glacier contribution to the freshwater inflow to the Arctic Ocean has been increasing, and this increase will affect many aspects of the arctic climate system. Increasing summer runoff to large Asian rivers and high-elevation glacierized watersheds in both Americas is important for agriculture and human needs, but this release of water from ice storage may diminish in the future as the relatively small high-mountain glaciers begin to disappear.

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